1. Field of the Invention
This invention relates to a method for forming a thin film, particularly to a method for forming a thin film suitable for a secondary battery field usable for mobile electronic device and electric automobiles.
2. Related Art Statement
So far, a sol-gel method, a CVD method or a PVD method is employed as a thin film-forming method. These methods require a multi-stage process including a heating process, a high vacuum condition, or a high energy condition accompanied with a substrate-heating process or a plasma-generating process. Therefore, those methods require large scale and complicate apparatus, resulting in large cost and complicate operationality in use.
Moreover, the above high energy condition runs counter to global environmental protection, resource saving and energy saving. Therefore, a new thin film-forming method without the above high energy condition has been desired.
It is an object of the present invention to provide a new thin film-forming method not including a high energy condition due to firing, heating or plasma generation.
This invention relates to a method for forming a thin film comprising the steps of:
preparing a reactive solution by adding metallic powders or metallic compound powders into a blended solution,
setting an anode electrode and a cathode electrode in the reactive solution,
applying a given voltage between the anode electrode and the cathode electrode, thereby to synthesize a compound thin film including the components of the blended solution and the metallic powders or the metallic compound powders on the anode electrode.
The inventors related to the present invention have been intensely studied for developing a new thin film-forming method not including a high energy process. As a result, they have found out surprisingly that when a reactive solution is made of a blended solution in which a given substance is dissolved and a given metallic powders added into the blended solution, and then, a given voltage is applied between a cathode electrode and an anode electrode provided in the reactive solution, a compound thin film composed of the components of the blended solution and the metallic powders is formed on the anode electrode, which is not pre-treated and heated. Then, since the compound thin film exhibits crystallinity, it is turned out that the components are reacted and synthesized on the anode electrode to form the crystalline compound thin film.
On the other hand, when only a blended solution incorporating components of a compound thin film to be formed is employed without metallic powders or metallic compound powders, the compound thin film is not formed or is formed very slowly on the anode electrode.
That is, it is required in this invention to use a reactive solution made of a given blended solution and given metallic powders or metallic compound powders. As a result, a compound thin film is made of the components of the blended solution and the metallic powders or metallic compound powders.
This invention has been established on the basis of the discovery of the above fact.
In a preferred embodiment of the thin film-forming method of the present invention, a substrate made of a porous material is set on a surface of the anode electrode opposite to the cathode electrode. In this case, the components of the blended solution and the metallic powder or metallic compound powders pass through the substrate freely, and arrive at the surfaces of the substrate. Therefore, the components are directly reacted on the substrate, and thus, the compound thin film is directly synthesized from the above components on the surfaces of the substrate.
If the given voltage is not applied to the reactive solution, the compound thin film is not formed. Therefore, if the anode electrode is formed in a predetermined patterned shape, the compound thin film can be synthesized in a given pattern corresponding to the patterned anode electrode.
According to the thin film-forming method of the present invention, the crystalline compound thin film can be formed on the anode electrode or the porous substrate without a pre-treating process, etc.